The present invention relates generally to a rotary cone drill bit having multiple support arms with a spindle or journal extending from each support arm and a ball retaining system for rotatably mounting a respective cutter cone assembly thereon and more particularly an improved bearing system to increase downhole drilling performance of the associated drill bit.
Various types of rotary drill bits or rock bits may be used to form a borehole in the earth. Examples of such rock bits include roller cone drill bits or rotary cone drill bits used in drilling oil and gas wells. A typical roller cone drill bit includes a bit body with an upper portion adapted for connection to a drill string. A plurality of support arms, typically three, depends from the lower portion of the bit body with each support arm having a spindle or journal protruding radially inward and downward with respect to a projected axis of rotation of the bit body.
Conventional roller cone drill bits are typically constructed in three segments. The segments may be positioned together longitudinally with a welding groove between each segment. The segments may then be welded with each other using conventional techniques to form the bit body. Each segment also includes as associated support arm extending from the bit body. As enlarged cavity or passageway is typically formed in the bit body to receive drilling fluids from the drill string. U.S. Pat. No. 4,054,772 entitled Positioning System for Rock Bit Welding, shows a method and apparatus for constructing a three-cone rotary rock bit from three individual segments.
A cutter cone assembly is generally rotatably mounted on a respective spindle or journal. The cutter cone assembly typically has a cavity formed therein and sized to receive the respective spindle. Various types of bearings and/or bearing surfaces may be disposed or found between the exterior of the spindle and the interior of the cavity. A typical bearing system used to rotatably mount a cutter cone assembly on a spindle will include one or more radial bearings and one or more thrust bearings. The radial bearings will generally be located between the outside diameter of the spindle and interior surfaces of the cavity disposed adjacent thereto. Thrust bearings and/or thrust bearing surfaces will generally be located between the end of the spindle opposite from the associated support arm and adjacent portions of the cavity formed in the cutter cone assembly. For some applications, a shoulder may be formed on the exterior of the spindle and a corresponding shoulder formed on the interior of the cavity with a thrust bearing and/or thrust bearing surfaces disposed therebetween.
The thrust bearings and/or the radial bearings may be formed as integral components of the spindle such as shown in U.S. Pat. No. 3,823,033 entitled Method for Making a Bearing System Having in Trained Wear-Resistant Particles. For some applications, roller type bearings may be disposed between the outside diameter of the spindle and adjacent portions of the cavity to support radial loads transmitted from the cutter cone assembly to the spindle. An example of such roller type bearings is shown in U.S. Pat. No. 3,952,815 entitled Land Krosion Protection for a Rock Cutter. U.S. Pat. No. 5,513,713 entitled Sealed and Lubricated Rotary Cone Drill Bit Having Improved Seal Protection shows multiple sets of roller type bearings disposed between a spindle and adjacent portions of a cavity. For other applications, a bushing may be disposed between the outside diameter of the spindle and adjacent portions of the cavity to carry such radial loads. Examples of such bushings are shown in U.S. Pat. No. 5,570,750 entitled Rotary Drill Bit With Improved Shirttail and Seal Protection and U.S. Pat. No. 5,593,231 entitled Hydrodynamic Bearings. These patents also disclose examples of thrust buttons or thrust bearings which may be disposed between the end of the spindle and adjacent portions of the cavity.
In a sealed rotary cone drill bit, lubricant under pressure is forced into a space formed between the exterior of the spindle and the interior of the cavity to cool and protect associated bearings and/or bearing surfaces. A lubricant reservoir is generally provided to compensate for any partial loss of lubricant and to balance internal lubricant pressure with external hydrostatic pressure during downhole drilling operation. The lubricant may comprise, for example, a calcium complex grease. Additionally, solids, such as molybdenum disulfide, may be added to the lubricant to increase the load carrying capacity of the bearings and/or bearing surfaces.
Bearings and bearing surfaces in a typical rotary cone drill bit are heavily loaded during downhole drilling operations. During such drilling operations, the drill bit is rotated in a borehole which causes the associate cutter cone assemblies to rotate on their respective spindles. The drill bit typically operates at a low speed with heavy weight applied to the bit which also produces a high load on the associated bearings. Rotary cone drill bits with sealed lubrication systems typically include one or more elastomeric seals which may be damaged from exposure to high temperatures created by excessive friction due to such heavy loads. Also, non-concentric rotation and/or wobbling of a cutter cone assembly on its respective spindle is another possible cause of seal damage. Seal failure from exposure to high temperatures or mechanical damage will eventually allow water, drilling fluids, and other debris from the drilling operation to penetrate the space between the cavity in the cutter cone assembly and the associated spindle and increase wear on the bearings and/or bearing surfaces to the point the cutter cone assemblies may be lost in the borehole.
U.S. Pat. No. 4,056,153 entitled Rotary Rock Bit with Multiple Row Coverage for Very Hard Formations, and U.S. Pat. No. 4,280,571 entitled Rock Bit, show examples of conventional rotary cone bits with cutter cone assemblies mounted on a spindle projecting from a support arm. Typically, ball bearings are inserted through an opening in an exterior surface of each support arm and a ball retainer passageway extending therefrom to rotatably secure each cutter cone assembly on its respective spindle. A ball retainer plug is then inserted into the ball retainer passageway. Finally, a ball plug weld is generally formed in the opening to secure the ball retainer plug within the ball retainer passageway.
Hardfacing of metal surfaces and substrates is a well-known technique to minimize or prevent erosion and abrasion of the metal surface or substrate. Hardfacing can be generally defined as applying a layer of hard, abrasion resistant material to a less resistant surface or substrate by plating, welding, spraying or other well known metal deposition techniques. Hardfacing is frequently used to extend the service life of drill bits and other downhole tools used in the oil and gas industry. Tungsten carbide and its various alloys are some of the more widely used hardfacing materials to protect drill bits and other downhole tools associated with drilling and producing oil and gas wells.
In accordance with teachings of the present invention, disadvantages and problems associated with previous rotary cone drill bits have been substantially reduced or eliminated. One aspect of the present invention includes providing a rotary cone drill bit having support arms and a spindle or journal extending from each support arm with a respective cutter cone assembly rotatably mounted thereon. The location of the mechanism which retains each cutter cone assembly on its respective spindle, such as ball bearings disposed between the exterior of the spindle and the interior of a cavity formed in each cutter cone assembly, is optimized to increase the effectiveness of both radial bearing components and thrust bearing components of the associated bearing system. For example, an exterior portion of each spindle may have a generally uniform outside diameter with a first radial bearing or bearing surface and a second radial bearing or bearing surface disposed thereon with a ball race formed in the exterior of the spindle between the first radial bearing and the second radial bearing. Dimensions of the first radial bearing relative to the second radial bearing may be selected in accordance with teachings of the present invention to increase load carrying capability of the associated bearing system and ability of the bearing system to prevent non-concentric rotation and/or wobble of the cutter cone assembly relative to its respective spindle. Teachings of the present invention may be used with a wide variety of mechanisms which hold a cutter cone assembly on a spindle in addition to ball bearings.
Technical benefits of the present invention include providing a rotary cone drill bit having a bearing system with increased load carrying capability which may be incorporated into existing support arm and cutter cone assemblies without substantially increasing or modifying the overall configuration of the support arm and cutter cone assembly. A bearing system incorporating teachings of the present invention generally maintains more concentric alignment during rotation of a cutter cone assembly onto its respective spindle and minimizes any tendency of the cutter cone assembly to wobble relative to the spindle. The present invention will prolong the downhole life of an associated rotary cone drill bit by increasing the load carrying capability of both radial bearing components and thrust bearing components of the associated bearing system. The present invention also provides a rotary cone drill bit in which the configuration and dimensions of the shirttail portion of each support arm may be increased to prolong the downhole life of the associated rotary cone drill bit.
Technical advantages of the present invention include the ability to apply hardfacing material on an enlarged shirttail portion of each support arm. Alternatively, the present invention allows increasing the number and/or size of inserts and compacts which may be installed within the shirttail portion of each support arm. Increasing the size of the shirttail portion of a support arm and covering the enlarged shirttail portion with a layer of hardfacing in accordance with teachings of the present invention may be particularly effective in increasing drill bit life during drilling of horizontal and/or directional well bores. Premature drill bit failure due to increased side loading of the associated drill and increased abrasion, erosion, and/or wear of the support arms may occur under such conditions. Multiple inserts and compacts may also be more securely installed within the shirttail portion of each support arm adjacent to the ball plug hole to further enhance abrasion, erosion and/or wear resistance.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.